Chip formation: Continuous chips with a built-up edge (BUE) typically form when machining which class of materials?

Introduction / Context:
Chip type reflects material behavior and cutting conditions. Continuous chips are associated with ductile plastic flow; built-up edge (BUE) forms when material adheres to the tool at low-to-moderate speeds, high friction, or insufficient lubrication. Recognizing when BUE is likely helps adjust parameters to improve finish and tool life.

Given Data / Assumptions:

• Conventional turning/milling operations.
• Uncoated tools at moderate speeds and feeds.
• Limited coolant or poor lubrication conditions.

Concept / Approach:
Ductile materials (e.g., low carbon steels, many aluminums at lower speeds) deform plastically and form continuous chips. Under certain conditions, adhesion at the tool–chip interface produces a BUE, which cyclically forms and breaks away, degrading surface finish and altering effective rake angle. Brittle materials, by contrast, tend to form discontinuous chips without a stable BUE.

Step-by-Step Solution:

Verification / Alternative check:
Machining handbooks describe typical chip types by material: ductile steels → continuous, with BUE if conditions favor adhesion; brittle cast irons → discontinuous chips without BUE dominance.

Why Other Options Are Wrong:

• Brittle/hard-only materials: usually produce segmented or discontinuous chips.
• “Soft metals only” is misleading; many soft metals are also ductile, but ductility is the governing factor, not “softness.”
• Composites display complex fracture-dominated removal, not continuous BUE chips.

Common Pitfalls:
Confusing softness with ductility; ignoring the role of speed and coolant; forgetting that high speeds can reduce BUE by increasing temperature and lowering adhesion time, especially with proper cutting fluids.

Final Answer:
ductile metals